5 Best Ways to Program to Check if One String Can Be Converted to Another by Removing One Element in Python

Rate this post

πŸ’‘ Problem Formulation: This article addresses the challenge of determining whether a string can be transformed into another string through the removal of a single element. For instance, given the input strings “coding” and “codng”, the desired output would be True since removing the ‘i’ from “coding” results in “codng”.

Method 1: Iterative Comparison

This method involves iteratively comparing characters of both strings. When the first mismatch is found, the method checks if the remainder of the string (except the mismatched character) matches the second string. It is straightforward and easy to understand.

Here’s an example:

def can_convert(str1, str2):
    if len(str1) != len(str2) + 1:
        return False
    for i in range(len(str1)):
        if str1[i] != str2[i]:
            return str1[i+1:] == str2[i:]
    return True

print(can_convert("coding", "codng"))

Output: True

This code snippet defines a function can_convert() that takes two strings and returns True if they can be matched by removing one character from the first string. It checks if the strings are of appropriate lengths, iterates through the characters, and compares them, returning the result accordingly.

Method 2: Using the ‘zip’ Function

This approach utilizes Python’s built-in zip function to pair characters from both strings and identify the point of divergence. It’s a Pythonic way of handling this problem and harnesses the power of tuple unpacking.

Here’s an example:

def can_convert_by_zip(str1, str2):
    diff = False
    for (char1, char2) in zip(str1, str2):
        if char1 != char2:
            if diff:
                return False
            diff = True
            str2 = str2[str2.index(char2):]
    return True

print(can_convert_by_zip("widget", "wdget"))

Output: True

The function can_convert_by_zip() iterates through each character pairing of the strings. Upon encountering a non-matching pair, it checks if a difference has been previously found. If so, it returns False. Otherwise, it removes the character from the second string and sets the flag that a difference has been found.

Method 3: List Comprehension

Here we employ Python’s list comprehension to create a list of boolean values indicating where the characters from the two strings match. The elegance of this method lies in its concise and direct way of creating a comparison list.

Here’s an example:

def can_convert_list_comp(str1, str2):
    return len(str1) == len(str2) + 1 and sum([s1 != s2 for s1, s2 in zip(str1, str2)]) == 1

print(can_convert_list_comp("bridge", "brdge"))

Output: True

The function can_convert_list_comp() checks if the length of the first string is exactly one character longer than the second. Then, it uses list comprehension combined with the zip function to compare characters, and finally, it verifies if there is exactly one mismatch.

Method 4: Using Regular Expressions

Regular expressions offer a powerful tool for pattern matching. In this method, a regex is created for each possible single character removal. It is suitable for those comfortable with regex operations but may be less readable for those unfamiliar with them.

Here’s an example:

import re

def can_convert_regex(str1, str2):
    for i in range(len(str1)):
        pattern = str1[:i] + '.' + str1[i+1:]
        if re.fullmatch(pattern, str2):
            return True
    return False

print(can_convert_regex("apple", "aple"))

Output: True

This code snippet imports Python’s re module and defines a function can_convert_regex(). It loops through each character index of the first string to generate a regex pattern that simulates the removal of that character and then checks if the second string fully matches this pattern.

Bonus One-Liner Method 5: Using ‘any’ Function

The any function in Python is employed to determine if at least one condition within an iterable is True. By coupling it with a generator expression, we create a compact one-liner method.

Here’s an example:

can_convert_one_liner = lambda str1, str2: any(str1[:i] + str1[i+1:] == str2 for i in range(len(str1)))

print(can_convert_one_liner("example", "exmple"))

Output: True

The one-liner can_convert_one_liner() is a lambda function that checks every possible single-character removal from the first string to see if it matches the second string. It uses the any function to return True as soon as a match is found.


  • Method 1: Iterative Comparison. Clear and easy to follow. However, it may not be the most efficient due to its linear approach.
  • Method 2: Using ‘zip’ Function. Pythonic and concise. It relies on the ability of the programmer to understand tuple unpacking and the zip function.
  • Method 3: List Comprehension. Direct comparison with a one-liner for the condition. It can be a bit abstract for beginners to grasp immediately.
  • Method 4: Using Regular Expressions. Offers a versatile approach. It can be complicated for those not well-versed in regex syntax.
  • Method 5: Using ‘any’ Function. This is a succinct solution. But, being a one-liner, it may sacrifice some readability for brevity.